There have been conventionally known tunnel boring machines that measure strain of rotational parts such as a cutter head. An example of such tunnel boring machines is disclosed in Japanese Utility Model Application Publication No. Sho 61-152097.
In the tunnel boring machine disclosed in Japanese Utility Model Application Publication No. Sho 61-152097, a strain sensor mounted on rotational parts such as a cutter head measures strain. The tunnel boring machine advances forward by a thrust force of a thrust jack, while rotating the cutter head, thereby to bore a tunnel in the natural ground. While the force acting on the cutter head (cutter thrust force) is typically estimated by subtracting from the jack thrust force various resistances such as the frictional resistance between the outer periphery of the body and the natural ground, Japanese Utility Model Application Publication No. Sho 61-152097 describes obtaining the cutter thrust force more directly by using a strain measurement value.
In boring, the tunnel boring machine may straddle different strata or encounter buried objects or gravel. It is important to measure the cutter thrust force to prevent damage to the cutter head and the cutter driving unit and abnormal wear of cutter bits (boring edges).